The proposed research will test the hypothesis that expression of a scavenger lipoprotein pathway by luteal cells facilitates functional and structural luteal regression via cell-specific mechanisms. Two specific aims will be addressed: (1) to compare and contrast binding and internalization of native and modified-LDL by luteal cell subpopulations from non-regressing and regressing CL, and (2) to determine whether modified-LDL has luteolytic actions on luteal cell subpopulations in vitro. Uptake and metabolism of modified-LDL will be determined by analysis of uptake and degradation of isotope-labeled LDL by non-regressing and regressing luteal cells. Physiological function will be determined by investigating the effects of modified-LDL exposure on five parameters of luteal cell function, i.e. steroidogenesis, cyclic AMP production, protein kinase-C activity, intracellular calcium flux, and induction of apoptosis. Since the CL is comprised of multiple luteal cell types, cell-specific interactions will be addressed. The proposed study will provide the first detailed information regarding the potential role of the scavenger lipoprotein pathway in the function and regression of the corpus luteum.